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Subject: Re: Importance of L2 cache speed/size for diff programs (was:..Genius sp

Author: fca

Date: 07:58:17 08/12/98

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On August 12, 1998 at 07:29:11, Robert Hyatt wrote:

>my P5/233/mmx clocks in at about 70% of the speed of my
>P6/200 machine.  As I've said before, the P6/PII core logic is simply better
>with the instruction pool and speculative execution and register renaming and
>you-name-it.

Sure, all of us agree here.  But to view cache speed (especially) and size
differences as having an additive (i.e. multiplicative!) effect together with
core speed differences is IMO misleading.  If you have something that executes
instructions twice as fast, you need a cache that works twice as fast, simply to
keep pace (i.e. to prevent a bottleneck).  For lower frequency (as % of CPU
time) activity like hash accessing, L2 cache speed/size is therefore not so
important.

Which was my point to Tom, whom I believe(d) was attributing to L2 hit
differences part of the reasons for the 2.5x reported by blass uri between a
P200MMX and a P2/300 running Junior.  I assume L2 only gets stressed by hash
activity.

>But hashing has little to do with how a program performs on either, due to the
>relative infrequency of hash probes compared to all the other stuff like
>move generation and positional evaluation...

and which activities do not stress L2 cache, but live within L1. :-)

SUMMARISED VIEW OF FCA:  As long as L2 size/speed keep up with "core MHz ratios
times allowance for P-->P2 ", it is not relevant when trying to explain
differences in performance of (say) Junior on a P200MMX and a P2/300.

Q1.  Tom, are you disagreeing with me in any of this?
Q2.  Bob, ditto?

:-)

Kind regards

fca

SUMMARISED VIEW OF FCA:  As long as L2 size/speed keep up with "core MHz ratios
times allowance for P-->P2 ", it is not relevant when trying to explain
differences in performance of (say) Junior on a P200MMX and a P2/300.



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